The AntiPhospholipid Syndrome (APS) is a disorder of recurrent arterial or venous thromboses and recurrent fetal loss affecting a small population of young people. These patients are identified by production of relatively high levels of antibodies specific for negatively charged phospholipids. An ELISA assay system using cardiolipin as antigen has been the most popular method of measuring these antibodies. the use of this assay has been hampered by low specificity because of the frequency with which low levels of anticardiolipin (aCL) antibodies are produced in diseased and healthy individuals. In phase I or this SBIR project, the P.I. and collaborators sought to identify a phospholipid antigen or mixture of phospholipid antigens which would enable sensitive and specific identification f APS patients (compared to other patient groups in which false positive aCL tests are frequent). Phospholipid antigen coated plates were stable at 4 degrees C for prolonged periods of time making the use of these reagents in an ELISA kit feasible. In phase II, the P.I. plans to assemble, calibrate, and complete the design of a PS/PA kit. Kit materials will be carefully tested for stability.